Fatigue and cognitive fatigability in patients with chronic pain

OBJECTIVES

Fatigue is common in patients with chronic pain. Still, there is a lack of studies examining objectively measurable cognitive aspects of fatigue: cognitive fatigability (CF). We aimed to investigate the presence of CF in patients with chronic pain and its relation to self-rated fatigue, attention, pain characteristics, sleep disturbance, depression, and anxiety.

METHODS

Two hundred patients with chronic pain and a reference group of 36 healthy subjects underwent a comprehensive neuropsychological test battery, including measurement of CF with the Wechsler Adult Intelligence Scale-III Coding subtest, and self-assessment of trait and state fatigue.

RESULTS

The patients with chronic pain did not show more CF as compared to the reference group. There was an association between CF and processing speed on a test of sustained and selective attention in the chronic pain group, while self-rated fatigue measures and pain characteristics were not associated with CF. Self-rated fatigue measures were highly correlated with self-rated pain intensity, spreading of pain, depression, anxiety, and sleep disturbance.

CONCLUSIONS

The findings highlight the distinction between objective and subjective aspects of fatigue in chronic pain, and that the underlying causes of these different aspects of fatigue need to be studied further.

Validating the Fatigue Scale for Motor and Cognitive Function (FSMC) in chronic stroke

BACKGROUND

Post-stroke fatigue can manifest as both physical and mental fatigue. The Fatigue Scale for Motor and Cognitive Functions (FSMC) evaluates fatigue on the motor and cognitive domains separately, however, the psychometric properties of this measure in stroke have not been reported.

OBJECTIVE

To determine the internal consistency, test-retest reliability, and concurrent validity of the FSMC in chronic stroke.

METHODS

Thirty-four participants with chronic stroke (55.26±12.27 years of age; 59.53±89.21 months post-stroke) completed the FSMC on two separate visits. Internal consistency and reliability of the FSMC were examined using Cronbach's alpha and two-way mixed effects intraclass correlation coefficients (ICC), respectively. Correlation between the FSMC and the Fatigue Severity Scale and Visual Analog Scale-Fatigue was used to assess concurrent validity.

RESULTS

Internal consistency was excellent (Cronbach's alpha > 0.9) and reliability was moderate to good (ICC = 0.72-0.81) for all FSMC scores. The FSMC demonstrated moderate to good concurrent validity with the Fatigue Severity Scale (ρ= 0.66-0.72) but only fair concurrent validity with the Visual Analog Scale-Fatigue (ρ= 0.37-0.44).

CONCLUSION

The FSMC is a valid and reliable measure of post-stroke fatigue and may be a useful tool to examine physical fatigue and cognitive fatigue in chronic stroke.

Predictors of performance and perceived fatigability in people with multiple sclerosis

BACKGROUND AND OBJECTIVE

Fatigability is a distinct construct from fatigue that has been reported to contribute to activity limitations in people with multiple sclerosis (PwMS). Identifying predictors of performance and perceived fatigability may guide the development of interventions to mitigate fatigability. This study investigated predictors of performance and perceived fatigability among PwMS.

METHODS

PwMS (N = 51) completed self-report measures of demographics, clinical history, symptoms severity (Modified Fatigue Impact Scale), and functioning (PROMIS Physical Function and PROMIS Cognitive Function Abilities). Performance fatigability measures included Ambulatory Fatigue Index (AFI), Deceleration Index (DI), and Distance Walking Index (DWI). Perceived fatigability measures included Pittsburgh Fatigability Scale (PFS), Perceived Physical Exertion, and Perceived Fatigue Intensity. Performance and perceived fatigability measures were calculated based on the Timed 25-Foot Walk Test and the 6-Minute Walk Test.

RESULTS

Multivariable linear regression analyses indicated that PROMIS Cognitive Function was a significant independent predictor of performance fatigability measured with AFI (β = -0.515, p = 0.007), DI (β = -0.511, p = 0.008), and DWI (β = -0.516, p = 0.007). Regarding perceived fatigability, PROMIS Pain Intensity predicted Perceived Fatigue Intensity (β = 0.325, p = 0.035). PROMIS Physical Function predicted PFS Mental fatigability (β = -0.503, p < 0.001). PROMIS Physical Function (β = -0.619, p < 0.001) and Cognitive Function (β = -0.249, p = 0.037) predicted PFS Physical fatigability.

CONCLUSIONS

Preliminary findings suggest that self-reported functioning levels, including physical and perceived cognitive function, are potential predictors of performance and perceived fatigability in MS. Notably, perceived fatigue impact showed no association with performance or perceived fatigability. Future studies are warranted to confirm and extend our findings.

Reduced clinical connectome fingerprinting in multiple sclerosis predicts fatigue severity

BACKGROUND

Brain connectome fingerprinting is progressively gaining ground in the field of brain network analysis. It represents a valid approach in assessing the subject-specific connectivity and, according to recent studies, in predicting clinical impairment in some neurodegenerative diseases. Nevertheless, its performance, and clinical utility, in the Multiple Sclerosis (MS) field has not yet been investigated.

METHODS

We conducted the Clinical Connectome Fingerprint (CCF) analysis on source-reconstructed magnetoencephalography signals in a cohort of 50 subjects: twenty-five MS patients and twenty-five healthy controls.

RESULTS

All the parameters of identifiability, in the alpha band, were reduced in patients as compared to controls. These results implied a lower similarity between functional connectomes (FCs) of the same patient and a reduced homogeneity among FCs in the MS group. We also demonstrated that in MS patients, reduced identifiability was able to predict, fatigue level (assessed by the Fatigue Severity Scale).

CONCLUSION

These results confirm the clinical usefulness of the CCF in both identifying MS patients and predicting clinical impairment. We hope that the present study provides future prospects for treatment personalization on the basis of individual brain connectome.

Subjective valuation of performance feedback is robust to trait cognitive fatigue in multiple sclerosis

BACKGROUND

Performance feedback is vital to rehabilitation interventions that treat cognitive impairments from multiple sclerosis (MS). Optimal treatment relies on participants' motivation to learn from feedback throughout these interventions. Cognitive fatigue, a prevalent symptom of MS, is associated with aberrant reward processing, which necessitates research into how fatigue affects perceived reward value of feedback in these individuals. The current study investigated how trait fatigue influences subjective valuation of feedback and subsequent feedback-seeking behavior in people with MS.

METHODS

33 MS and 32 neurotypical (NT) participants completed a willingness-to-pay associative memory paradigm that assessed feedback valuation via trial-by-trial decisions to either purchase or forego feedback in service of maximizing a performance-contingent monetary reward. Participant ratings of trait fatigue were also collected. Generalized logistic mixed modeling was used to analyze factors that influenced trial-wise feedback purchase decisions and task performance.

RESULTS

Despite reporting greater trait fatigue, MS participants purchased comparable amounts of feedback as NT participants. Like NT participants, MS participants were more likely to purchase feedback when they were less confident about response accuracy. MS participants also performed comparably to NT participants, who both particularly benefited from purchase decisions that yielded negative feedback (i.e., indicating a response error).

CONCLUSIONS

Trait cognitive fatigue may not impact performance feedback valuation in people with MS. Nonetheless, confidence in performance may drive their feedback-seeking behavior and may serve as a target for improving learning throughout cognitive rehabilitation and maximizing treatment success.

Role of selective attention in fatigue in neurological disorders

BACKGROUND

Chronic fatigue is a significant symptom in several diseases including traumatic and degenerative neurological disorders. While several studies have investigated the correlates of chronic fatigue, there is as yet no unifying framework to explain chronic fatigue.

METHODS

In this narrative review, I investigate the role of selective attention in the development of chronic fatigue and discuss results within the framework of the sensory attenuation model of fatigue, which posits that fatigue is the phenomenological output of altered attention to sensory input. Following a short introduction of this framework, I present results from investigations that address attentional mechanisms in fatigue in multiple sclerosis, stroke, traumatic brain injury and Parkinson's disease.

RESULTS

Attention was quantified in all four disease models using a variety of outcome measures, including behavioural, neurophysiological, structural and functional brain connectivity. The range of measures precluded direct comparison of results across disease conditions; however, in all four disease models there was evidence of poor selective attention that explained levels of chronic fatigue, supporting the sensory attenuation model of fatigue as a disease-independent mechanism of fatigue. Evidence was lacking to draw any conclusions about the direction of causality.

CONCLUSION

The role of selective attention in development of fatigue is indicated. Future studies must focus on establishing causality and exploring attentional circuitry as a potential therapeutic target.

Fatigue and Human Performance: An Updated Framework

Fatigue has been defined differently in the literature depending on the field of research. The inconsistent use of the term fatigue complicated scientific communication, thereby limiting progress towards a more in-depth understanding of the phenomenon. Therefore, Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) proposed a fatigue framework that distinguishes between trait fatigue (i.e., fatigue experienced by an individual over a longer period of time) and motor or cognitive task-induced state fatigue (i.e., self-reported disabling symptom derived from the two interdependent attributes performance fatigability and perceived fatigability). Thereby, performance fatigability describes a decrease in an objective performance measure, while perceived fatigability refers to the sensations that regulate the integrity of the performer. Although this framework served as a good starting point to unravel the psychophysiology of fatigue, several important aspects were not included and the interdependence of the mechanisms driving performance fatigability and perceived fatigability were not comprehensively discussed. Therefore, the present narrative review aimed to (1) update the fatigue framework suggested by Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) pertaining the taxonomy (i.e., cognitive performance fatigue and perceived cognitive fatigue were added) and important determinants that were not considered previously (e.g., effort perception, affective valence, self-regulation), (2) discuss the mechanisms underlying performance fatigue and perceived fatigue in response to motor and cognitive tasks as well as their interdependence, and (3) provide recommendations for future research on these interactions. We propose to define motor or cognitive task-induced state fatigue as a psychophysiological condition characterized by a decrease in motor or cognitive performance (i.e., motor or cognitive performance fatigue, respectively) and/or an increased perception of fatigue (i.e., perceived motor or cognitive fatigue). These dimensions are interdependent, hinge on different determinants, and depend on body homeostasis (e.g., wakefulness, core temperature) as well as several modulating factors (e.g., age, sex, diseases, characteristics of the motor or cognitive task). Consequently, there is no single factor primarily determining performance fatigue and perceived fatigue in response to motor or cognitive tasks. Instead, the relative weight of each determinant and their interaction are modulated by several factors.

Altered functional connectivity during performance feedback processing in multiple sclerosis

Effective learning from performance feedback is vital for adaptive behavior regulation necessary for successful cognitive performance. Yet, how this learning operates in clinical groups that experience cognitive dysfunction is not well understood. Multiple sclerosis (MS) is an autoimmune, degenerative disease of the central nervous system characterized by physical and cognitive dysfunction. A highly prevalent impairment in MS is cognitive fatigue (CF). CF is associated with altered functioning within cortico-striatal regions that also facilitate feedback-based learning in neurotypical (NT) individuals. Despite this cortico-striatal overlap, research about feedback-based learning in MS, its associated neural underpinnings, and its sensitivity to CF, are all lacking. The present study investigated feedback-based learning ability in MS, as well as associated cortico-striatal function and connectivity. MS and NT participants completed a functional magnetic resonance imaging (fMRI) paired-word association task during which they received trial-by-trial monetary, non-monetary, and uninformative performance feedback. Despite reporting greater CF throughout the task, MS participants displayed comparable task performance to NTs, suggesting preserved feedback-based learning ability in the MS group. Both groups recruited the ventral striatum (VS), caudate nucleus, and ventromedial prefrontal cortex in response to the receipt of performance feedback, suggesting that people with MS also recruit cortico-striatal regions during feedback-based learning. However, compared to NT participants, MS participants also displayed stronger functional connectivity between the VS and task-relevant regions, including the left angular gyrus and right superior temporal gyrus, in response to feedback receipt. Results indicate that CF may not interfere with feedback-based learning in MS. Nonetheless, people with MS may recruit alternative connections with the striatum to assist with this form of learning. These findings have implications for cognitive rehabilitation treatments that incorporate performance feedback to remediate cognitive dysfunction in clinical populations.

Neural mechanisms underlying state mental fatigue: a systematic review and activation likelihood estimation meta-analysis

Sustained performance of cognitive tasks could lead to the development of state mental fatigue characterized by subjective sensation of mental weariness and decrease in cognitive performance. In addition to the occupational hazards associated with mental fatigue, it can also affect physical performance reducing endurance, balance, and sport-specific technical skills. Similarly, mental fatigue is a common symptom in certain chronic health conditions such as multiple sclerosis affecting quality of life of the patients. Despite its widely acknowledged negative impact, the neural mechanisms underlining this phenomenon are still not fully understood. We conducted a systematic review and activation likelihood estimation (ALE) meta-analysis of functional neuroimaging studies investigating the effect of mental fatigue due to time-on-task (TOT) on brain activity to elucidate the possible underlying mechanisms. Studies were included if they examined change in brain activity induced by experimental mental fatigue (TOT effect) or investigated the relationship between brain activity and subjective mental fatigue due to TOT. A total of 33 studies met the review's inclusion criteria, 13 of which were included in meta-analyses. Results of the meta-analyses revealed a decrease in activity with TOT in brain areas that constitute the cognitive control network. Additionally, an increased activity with TOT, as well as negative relationship with subjective mental fatigue was found in parts of the default mode network of the brain. The changes in cognitive control and the default mode networks of the brain due to state mental fatigue observed in this study were discussed in relation to the existing theories of mental fatigue.

Memory-Guided Reaching: Is It Effortful?

We previously showed that perceived effort during visually guided reaching was altered as task demand varied. Further, self-reported subjective fatigue correlated with perceived effort and reach performance under visually guided conditions. Memory-guided reaching often leads to performance deterioration and can provide insights about the planning and control of reach actions. It is unclear how perceived effort changes during memory-guided reaching and whether self-reported subjective fatigue is associated with perceived effort of memory-guided reaching. Twenty-three young adults performed reach actions under visually- and memory-guided conditions. Perceived effort, reaction time, and endpoint error increased significantly from the visually- to the memory-guided condition. Self-reported subjective fatigue was associated with perceived effort and reach distance error during memory-guided reaching; those with higher levels of fatigue reported greater perceived effort and tended to reach farther when visual information was not available. These findings establish a foundation to examine relationships between subjective fatigue, perceived effort, and reach control.

Current perspectives on the diagnosis and management of fatigue in multiple sclerosis

INTRODUCTION

Fatigue is a common and debilitating symptom among multiple sclerosis (MS) patients with a prevalence up to 81% and with a considerable impact on quality of life. However, its subjective nature makes it difficult to define and quantify in clinical practice. Research aimed at a more precise definition and knowledge of this construct is thus continuously growing.

AREAS COVERED

This review summarizes the most relevant updates available on PubMed up to July 1^st 2022 regarding: the assessment methods that aim to measure the concept of fatigue (as opposed to fatigability), the possible treatment pathways currently available to clinicians, interconnection with the pathophysiological substrates and with the common comorbidities of MS, such as depression and mood disorders.

EXPERT OPINION

The in-depth study of fatigue can help to better understand its actual impact on MS patients and can stimulate clinicians towards a more valid approach, through a targeted analysis of this symptom. Considering fatigue from a multidimensional perspective allows the use of patient-tailored methods for its identification and subsequent treatment by different professional figures. Better identification of methods and treatment pathways would reduce the extremely negative impact of fatigue on MS patients' quality of life.

Task- and resting-state fMRI studies in multiple sclerosis: From regions to systems and time-varying analysis. Current status and future perspective

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Functional MRI is able to detect adaptive and maladaptive abnormalities at different MS stages.

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Increased fMRI activity is a feature of early MS, while progressive exhaustion of adaptive mechanisms is detected later on in the disease.

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Collapse of long-range connections and impaired hub integration characterize MS network reorganization.

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Time-varying connectivity analysis provides useful and complementary pieces of information to static functional connectivity.

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New perspectives might be the use of multimodal MRI and artificial intelligence.

Multiple sclerosis (MS) is a neurological disorder affecting the central nervous system and features extensive functional brain changes that are poorly understood but relate strongly to clinical impairments. Functional magnetic resonance imaging (fMRI) is a non-invasive, powerful technique able to map activity of brain regions and to assess how such regions interact for an efficient brain network. FMRI has been widely applied to study functional brain changes in MS, allowing to investigate functional plasticity consequent to disease-related structural injury. The first studies in MS using active fMRI tasks mainly aimed to study such plastic changes by identifying abnormal activity in salient brain regions (or systems) involved by the task. In later studies the focus shifted towards resting state (RS) functional connectivity (FC) studies, which aimed to map large-scale functional networks of the brain and to establish how MS pathology impairs functional integration, eventually leading to the hypothesized network collapse as patients clinically progress. This review provides a summary of the main findings from studies using task-based and RS fMRI and illustrates how functional brain alterations relate to clinical disability and cognitive deficits in this condition. We also give an overview of longitudinal studies that used task-based and RS fMRI to monitor disease evolution and effects of motor and cognitive rehabilitation. In addition, we discuss the results of studies using newer technologies involving time-varying FC to investigate abnormal dynamism and flexibility of network configurations in MS. Finally, we show some preliminary results from two recent topics (i.e., multimodal MRI analysis and artificial intelligence) that are receiving increasing attention. Together, these functional studies could provide new (conceptual) insights into disease stage-specific mechanisms underlying progression in MS, with recommendations for future research.

The Neurobiology of Pathological Fatigue: New Models, New Questions

The last decade has seen the emergence of new theoretical frameworks to explain pathological fatigue, a much neglected, yet highly significant symptom across a wide range of diseases. While the new models of fatigue provide new hypotheses to test, they also raise a number of questions. The primary purpose of this essay is to examine the predictions of three recently proposed models of fatigue, the overlap and differences between them, and the evidence from diseases that may lend support to the models of fatigue. I also present expansions for the sensory attenuation model of fatigue. Further questions examined here are the following: What are the neural substrates of fatigue? How can sensory attenuation, which underpins agency also explain fatigue? Are fatigue and agency related?

State and Trait Fatigue and Energy Predictors of Postural Control and Gait

Compromised attentional resources during perceived fatigue has been suggested to alter motor control. The authors determined if measures of postural control and gait are predicted by state and trait physical and mental fatigue and energy, and how these relationships are modified by sex, sleep quality, and physical activity. Young adults (n = 119) completed the Modified Clinical Test of Sensory Integration, overground walking, and questionnaires to quantify fatigue and energy, sleep quality, and physical activity. Regression models indicated that trait fatigue, trait energy, and sleep quality were predictors of postural control (p ≤ .02, R2 ≥ .04). State fatigue, state energy, and sex were predictors of gait (p ≤ .05, R2 ≥ .03). While the variance explained was low (3-13%), the results demonstrate perceptions of fatigue and energy may influence posture and gait.

Neuroimaging markers of chronic fatigue in older people: a narrative review

BACKGROUND

Chronic fatigue is a common symptom in older adults. Although some studies have attempted to identify the neuronal correlates of fatigue associated with chronic diseases, the scientific evidence is scarce regarding fatigue in older people not suffering from a specific disease.

AIMS

To gather available evidence of neuroimaging studies investigating the associations between fatigue and brain health in older adults out of the context of a specific disease, and to identify potential brain structures associated with this symptom.

METHODS

Studies considering exclusively patients with a specific disease and/or studies focusing on physiological mechanisms of acute fatigue induced by the realization of cognitive and physical tasks were excluded.

RESULTS

Very few studies on the associations of fatigue with neuroimaging markers are currently available. Fatigue was associated with reduced hippocampus volumes and with hippocampal amyloid deposition. Regarding the association between fatigue and the circuit of basal ganglia, putamen and thalamus were associated with physical fatigability, whereas amygdala and thalamus with mental fatigability. Very limited evidence about white matter integrity found that healthy individuals with high levels of fatigue had a greater total volume of leukoaraiosis.

CONCLUSION

This review suggests that hippocampus damage and potentially loss of function in basal ganglia networks could play a role on chronic fatigue during aging. Further studies are needed to assess the associations of fatigue with white matter alterations.

Perceived effort for reaching is associated with self-reported fatigue

Perceived effort for goal-directed reaching may be impacted by the level of self-reported fatigue, however, the relationship between self-reported fatigue and perceived effort has not been examined. We examined how perceived effort changed under varied reach conditions and the relationship between fatigue, perceived effort and reach performance. Twenty-three young adults performed reach actions toward 9 different targets on a digitizing tablet. Perceived effort was measured using the Borg Rate of Perceived Exertion and Paas Mental Effort Rating Scale. Self-reported fatigue was quantified using the Fatigue Scales for Motor and Cognitive Functions. As reach conditions became more difficult, perceived effort increased significantly. Further, individuals who reported greater fatigue also reported greater perceived effort and showed greater endpoint error during reaching.

Anatomical Covariance Analysis: Detection of Disrupted Correlation Network Related to Clinical Trait Fatigue in Multiple Sclerosis: A Pilot Study

Background

Fatigue is one of the most distressing symptoms among persons with multiple sclerosis (PwMS). The experience of fatigue is inherently interoceptive, yet no study to date has explicitly investigated the insular cortex (IC) as a primary goal in the experience of fatigue in PwMS. In addition, it is unknown how brain regions such as IC play a role in state or trait fatigue.

Objective

Assess the involvement of the IC in trait fatigue and state fatigue in PwMS with and without clinical fatigue.

Methods

Trait and state fatigue, cognitive status, and structural MRI were assessed in 27 PwMS. PwMS were stratified into nonclinical fatigue (nF-MS, FSS ≤ 4.0) (n = 10) and clinical fatigue (F-MS, FSS ≥ 5.0) (n = 10). Voxel-based morphometry analysis (VBM) for the whole sample (n = 20) and for the two groups was performed. Anatomical covariance analysis (ACA) analysis was conducted by selecting different volumes included in the corticostriatal network (CoStN) and analyzing interhemispheric correlations between those volumes to explore the state of the CoStN in both groups.

Results

In the VBM analysis, when considering the whole sample of PwMS, higher levels of trait fatigue were negatively associated with grey matter (GM) volume in the left dorsal anterior insula (dAI) (rho = −0.647; p = 0.002; R² = 0.369). When comparing nF-MS versus F-MS, significant differences were found in the left dAI, where the F-MS group showed less GM volume in the left dAI. In the ACA analysis, the F-MS group showed fewer significant interhemispheric correlations in comparison with the Low-FSS group.

Conclusions

The present results provide support to the interoceptive component of self-reported fatigue and suggest that changes in the relationship between the different anatomical regions involved in the CoStN are present even in nonclinical trait fatigue. Those changes might be responsible for the experience of trait fatigue in PwMS. Future studies with larger samples and multimodal MRI acquisitions should be considered to fully understand the changes in the CoStN and the specific role of the IC in trait fatigue.

Oculomotor Fatigue and Neuropsychological Assessments mirror Multiple Sclerosis Fatigue

Fatigue is a major complaint in MS. Up to now no objective assessment tools have been established which hampers any treatment approach. Previous work has indicated an association of fatigue with cognitive measures of attention. Oculomotor tests have been established in healthy individuals as a read-out of fatigue, and to some extent in MS patients. Based on these observations we compared two groups of MS patients, one with fatigue (n=28) and one without fatigue (n=21) and a group of healthy subjects (n=15) with a standardised computerised measure of alertness and an oculomotor stress test. Patients with fatigue showed highly significant changes of their saccade dynamics as defined by the Main Sequence and Phase Plane plots: They showed slowing of saccades, the characteristical fatigue double peak, and an asymmetrical phase plane. Oculomotor tests differentiated significantly between fatigue and fatigabiliy in our MS patients. They also showed significantly worse performance in the alertness test as well as in the oculomotor task. Significantly slower reaction times were observed for tonic alertness in 2 series without a cue (p=.025 and p=.037) but not in phasic alertness with a cue (p=.24 and p=.34). Performance was influenced by disability as well as by affective state. We conclude, when controlling for disability and depression, saccadic stress tests and alertness tests could be used as an objective read-out for fatigability and fatigue in MS patients.

Changes in plant function and root mycobiome caused by flood and drought in a riparian tree

Under increasingly harsh climatic conditions, conservation of threatened species requires integrative studies to understand stress tolerance. Riparian Ulmus minor Mill. populations have been massively reduced by Dutch Elm disease (DED). However, resistant genotypes were selected to restore lost populations. To understand the acclimation mechanisms to the succession of abiotic stresses, ramets of five DED-tolerant U. minor genotypes were subjected to flood and subsequently to drought. Physiological and biochemical responses were evaluated together with shifts in root-fungal assemblages. During both stresses, plants exhibited a decline in leaf net photosynthesis and an increase in percentage loss of stem hydraulic conductivity and in leaf and root proline content. Stomatal closure was produced by chemical signals during flood and hydraulic signals during drought. Despite broad similarities in plant response to both stresses, root-mycobiome shifts were markedly different. The five genotypes were similarly tolerant to moderate drought, however, flood tolerance varied between genotypes. In general, flood did not enhance drought susceptibility due to fast flood recovery, nevertheless, different responses to drought after flood were observed between genotypes. Associations were found between some fungal taxonomic groups and plant functional traits varying with flood and drought (e.g. proline, chlorophyll and starch content) indicating that the thriving of certain taxa depends on host responses to abiotic stress.

Cognitive Fatigability is Independent of Subjective Cognitive Fatigue and Mood in Multiple Sclerosis

BACKGROUND

Sustained cognitive testing is used to detect cognitive fatigability and is often considered a substitute for subjective cognitive fatigue (CF). However, the relationship between cognitive fatigability and subjective CF in people with multiple sclerosis (PwMS) remains undetermined.

OBJECTIVE

To explore potential associations between fatigability induced by sustained cognitive testing and subjective CF in PwMS.

METHODS

We gave 120 PwMS and 60 demographically matched, healthy individuals the Beck Depression Inventory-FastScreen (BDI-FS) to measure mood and the Modified Fatigue Impact Scale to measure CF. In addition, we used the Quotient ADHD Test, a sustained attention test, to measure cognitive fatigability. We also explored potential correlations between the individuals' performance on the sustained attention test and thalamic volume using recent MRI scans.

RESULTS

Forty-one (34.2%) of the PwMS exhibited cognitive fatigability. These 41 were found to be significantly older (P=0.006), had been diagnosed with the disease for longer (P=0.03), had higher scores (P<0.001) on the Expanded Disability Status Scale, and had reduced thalamic volume (P=0.04) compared with the 79 (65.8%) PwMS not exhibiting cognitive fatigability. The PwMS exhibiting cognitive fatigability scored similarly on the BDI-FS (P=0.21) and self-reported similar rates of CF (P=0.62) as the PwMS not exhibiting cognitive fatigability.

CONCLUSION

Cognitive fatigability induced by sustained cognitive testing is not an accurate clinical alternative to subjective CF. This study provides evidence to support cognitive fatigability and CF in PwMS as two distinct concepts.

Association Between Fatigue and Motor Exertion in Patients With Multiple Sclerosis-a Prospective Study

Background: Fatigue in multiple sclerosis (MS) is conceived as a multidimensional construct.

Objectives: This study aims to describe the changes of balance and gait parameters after 6 min of walking (6 MW) as potential quantitative markers for perceptions of state fatigue and trait fatigue in MS.

Methods: A total of 19 patients with MS (17 with fatigue) and 24 healthy subjects underwent static posturography, gait analysis, and ratings of perceived exertion before and after 6 MW.

Results: 6 MW was perceived as exhaustive, but both groups featured more dynamic comfortable speed walking after 6 MW. Shorter stride length at maximum speed and increased postural sway after 6 MW indicated fatigability of balance and gait in MS group only. While most changes were related to higher levels of perceived exertion after 6 MW (state fatigue), higher fatigue ratings (trait fatigue) were only associated with less increase in arm swing at comfortable speed. Further analysis revealed different associations of trait fatigue and performance fatigability with disability and motor functions. Performance fatigability was most closely related to the Expanded Disability Status Scale, while for trait fatigue, the strongest correlations were seen with balance function and handgrip strength.

Conclusions: Fatigability of performance was closely related to perceptions of exertion after 6 MW (state fatigue) and disability in MS but distinct from fatigue ratings, conceived as trait fatigue. Our study identified postural sway, arm swing during gait, and hand grip strength as unexpected potential motor indicators of fatigue ratings in MS.

Cognitive fatigability is a quantifiable distinct phenomenon in multiple sclerosis

Cognitive fatigability in multiple sclerosis represents the decrease in cognitive performance over time. It is a frequent symptom that negatively affects quality of life and ability to work. There are no objective measures of cognitive fatigability. This study aimed at quantifying cognitive fatigability despite the learning effect and to clarify whether cognitive fatigability represents a free-standing phenomenon rather than an aspect of cognitive impairment. We measured information processing speed with the Symbol Digit Modalities Test, and the number of right answers was recorded every 30 s for 180 s. We approximated the number of right answers as function of time with two logarithmic models, one including a first-order term alone and the other adding also a second-order term. The coefficient of the latter (B) may quantify performance deflection and may represent cognitive fatigability. We tested 173 patients with multiple sclerosis, including 119 cognitively impaired and 54 cognitively preserved patients, and 35 healthy subjects. The performance of cognitively preserved patients showed a deflection at the end of task that was detected neither in controls nor in cognitively impaired patients and needed a second-order term to be approximated (p < .03, F = 14.02). B was explained neither by depression nor fatigue. We proposed for the first time a method to quantify cognitive fatigue via a second-order least square fit model, easily usable in the clinical practice. By using this novel approach, cognitive fatigability results to be a free-standing phenomenon that is more evident in cognitively preserved than in cognitive impaired patients.

Insula and putamen centered functional connectivity networks reflect healthy agers' subjective experience of cognitive fatigue in multiple tasks

Cognitive fatigue (CF) impairs ability to perform daily activities, is a common complaint of aging and a symptom of multiple neurological conditions. However, knowledge of the neural basis of CF is limited. This is partially because CF is difficult to systematically modulate in brain imaging experiments. The most common approach has been to scan brain activity during effortful cognitive tasks. Consequently, neural correlates of CF tend to be task-specific and may vary across tasks. This makes it difficult to know how results generalize across studies and is outside the subjective experience of CF which tends to be similar in different tasks. It has been hypothesized that the subjective experience of CF might arise from domain general systems monitoring and acting on energy depletion in task specific circuits. Direct supporting neural evidence is lacking. By repeatedly scanning aging individuals undertaking four different tasks using functional Magnetic Resonance Imaging and referencing scans to detailed CF self-ratings taken before and after scanning, we sought task-general correlates of CF. We ran a data-driven representational similarity analysis, treating each brain region as a candidate CF functional connectivity hub, and correlating inter-participant differences in hub-based connectivity patterns with inter-participant differences in self-rated CF-profiles (a pattern of ratings across 18 questions). Both right insula and right putamen-based network connectivity patterns reflected CF across all tasks and could underpin subjective experience of CF.

Cognitive Fatigue in Multiple Sclerosis: An Objective Approach to Diagnosis and Treatment by Transcranial Electrical Stimulation

Cognitive fatigue is one of the most frequent symptoms in multiple sclerosis (MS), associated with significant impairment in daily functioning and quality of life. Despite its clinical significance, progress in understanding and treating fatigue is still limited. This limitation is already caused by an inconsistent and heterogeneous terminology and assessment of fatigue. In this review, we integrate previous literature on fatigue and propose a unified schema aiming to clarify the fatigue taxonomy. With special focus on cognitive fatigue, we survey the significance of objective behavioral and electrophysiological fatigue parameters and discuss the controversial literature on the relationship between subjective and objective fatigue assessment. As MS-related cognitive fatigue drastically affects quality of life, the development of efficient therapeutic approaches for overcoming cognitive fatigue is of high clinical relevance. In this regard, the reliable and valid assessment of the individual fatigue level by objective parameters is essential for systematic treatment evaluation and optimization. Transcranial electrical stimulation (tES) may offer a unique opportunity to manipulate maladaptive neural activity underlying MS fatigue. Therefore, we discuss evidence for the therapeutic potential of tES on cognitive fatigue in people with MS.

Exercise in Multiple Sclerosis: Knowing is Not Enough-The Crucial Role of Intention Formation and Intention Realization

A large body of evidence supports the notion that patients with multiple sclerosis (MS) benefit from physical exercise. However, this research-based recommendation has been insufficiently translated into practice. In this commentary article, we highlight the psychological evidence for the intention-behaviour gap and discuss evidence-based recommendations for bridging this gap, with the aim to change behaviour in MS patients. It is accepted that psychological research distinguishes intention formation from intention realization and that these processes have to be considered when the aim is to enhance physical activity in MS patients. We suggest that the transtheoretical model of behaviour change is a useful and general framework for examining the process of intention formation and that a MS-specific perspective is more useful for realizing exercise intention. MS patients are faced with severe self-control demands that hinder the realization of sport and exercise goals. Specifically, MS patients experience fatigue, which imposes substantial self-control demands. Here, we suggest implementation intention as an effective tool that aids in counteracting deficits in intention realization (getting started and staying on track). We also note that research knowledge is not sufficiently translated into clinical practice. Based on an interdisciplinary approach we recommend that therapists of MS patients should be more aware of psychological theories of health behaviour change and that they should use these to improve and optimize treatment approaches.

Capturing fatigue parameters: The impact of vagal processing in multiple sclerosis related cognitive fatigue

BACKGROUND

Causes of fatigue in Multiple Sclerosis remain elusive. Recently, we developed a model linking cognitive fatigue to inflammatory processes based on a neuroinflammatory reflex-arc instantiated by the vagus nerve. The relation between experienced autonomic dysfunctions, based on vagal processing, and cognitive fatigue is well-known, but an examination of the association of objectively measured vagal activity and cognitive fatigue is missing. An attempt was made to collect behavioral and physiological evidence that can be associated with experienced autonomic dysfunctions and fatigue in Multiple Sclerosis patients.

METHODS

Behavioral performance (response bias) and autonomic functioning (Heart rate variability and Skin conductance level) during an acoustic vigilance task were investigated in 53 Multiple Sclerosis patients. We assessed trait fatigue (independent from task), and time-on-task related increase of fatigue. Regression analysis was used to predict the fatigue status with physiological and behavioral scores.

RESULTS

Response bias, indicating a reduced responsiveness, and high and very low frequency components of Heart rate variability, indicating an increased parasympathetic activity, contribute to the regression of trait fatigue. Reduced Heart rate variability (SDNN) and increased parasympathetic activity (pNN50) remained in the regression model predicting time-on-task fatigue.

CONCLUSION

Cognitive fatigue in MS is related to parasympathetic activity and reduced responsiveness, supporting our model representing fatigue as inflammatory processes in the brain. Standardized subjective and objective autonomous dysfunction measures might be considered as additional assessments in MS.

Evaluation of MS related central fatigue using MR neuroimaging methods: Scoping review

BACKGROUND

Fatigue is a common and debilitating symptom in multiple sclerosis (MS). Over the past decade, a growing body of research has focussed on the pathophysiological mechanisms underlying central (cognitive and physical) fatigue in MS. The precise mechanisms causing fatigue in MS patients are complex and poorly understood, and may differ between patients. Advanced quantitative magnetic resonance imaging (MRI) techniques allow for objective assessment of disease pathology and have been used to characterise the pathophysiology of central fatigue in MS.

OBJECTIVE

To systematically review the existing literature of MRI-based studies assessing the pathophysiological mechanisms of MS-related central fatigue.

METHODS

A systematic literature search of four major databases (PubMed, Medline, Embase, Scopus and Google Scholar) was conducted to identify MRI-based studies of MS-related fatigue published in the past 20 years. Studies using the following MRI-based methods were included: structural (lesion load/atrophy), T1 relaxation time/magnetisation transfer ratio (MTR), diffusion tensor imaging (DTI), functional MRI (fMRI) and magnetic resonance spectroscopy (MRS).

RESULTS

A total of 92 studies were identified as meeting the search criteria and included for review. Structurally, regional gray/white matter atrophy, cortical thinning, decreased T1 relaxation times and reduced fractional anisotropy were associated with central fatigue in MS. Functionally, hyperactivity and reduced functional connectivity in several regional areas of frontal, parietal, occipital, temporal and cerebellum were suggested as causes of central fatigue. Biochemically, a reduction in N-acetyl aspartate/creatine and increased (glutamine+glutamate)/creatine ratios were correlated with fatigue severity in MS.

CONCLUSION

Several advanced quantitative MRI methods have been employed in the study of central fatigue in MS. Central fatigue in MS is associated with macro/microstructural and functional changes within specific brain regions (frontal, parietal, temporal and deep gray matter) and specific pathways/networks (cortico-cortical and cortico-subcortical). Alternations in the cortico-striatal-thalamocortical (CSTC) loop are correlated with the development of fatigue in MS patients.

Neural correlates of perceived physical and mental fatigability in older adults: A pilot study

This pilot work examined associations of brain grey matter volumes (GMV) with perceived fatigability in older adults to elucidate disablement mechanisms. A subsample (n = 29; age = 77.2 ± 5.5; 86% female) of participants from the Lifestyle Interventions and Independence for Elders (LIFE) Study was utilized to quantify GMV for regions of interest in the basal ganglia and limbic system normalized to intracranial volume. The Pittsburgh Fatigability Scale measured physical and mental fatigability (score 0-50; higher physical fatigability ≥ 15; higher mental fatigability ≥ 13). We used an exploratory alpha level of p < 0.1. Nineteen (66%) participants had higher physical fatigability, 19 (66%) had higher mental fatigability, of these, 17 (57%) had both. Right hippocampal volumes/ICV were smaller in participants with higher verses lower physical fatigability (0.261 ± 0.039 vs. 0.273 ± 0.022, p = 0.07); associations were similar for right putamen and bilateral thalamus. Higher mental fatigability was associated with smaller right hippocampus, thalamus, and posterior cingulum and bilateral amygdala. Higher fatigability in older adults may be associated with smaller volumes of the basal ganglia and limbic system, indicating mechanisms for further exploration.

Cerebellar and premotor activity during a non-fatiguing grip task reflects motor fatigue in relapsing-remitting multiple sclerosis

Fatigue is a common and highly disabling symptom of multiple sclerosis. Patients experience an effort-independent general subjective feeling of fatigue as well as excessive fatigability when engaging in physical or mental activity. Previous research using functional magnetic resonance imaging (fMRI) has revealed heterogeneous findings, but some evidence implicates the motor system. To identify brain correlates of fatigue, 44 mildly impaired patients with relapsing-remitting multiple sclerosis and 25 age- and gender-matched healthy controls underwent functional magnetic resonance imaging at 3 Tesla, while they performed alternating blocks of rest and a non-fatiguing precision grip task. We investigated neural correlates of fatigue using the motor subscore of Fatigue Scale for Motor and Cognitive Functions (FSMC_MOTOR) using the bilateral motor cerebellum, putamen, and dorsal premotor cortex as regions of interest. Patients and healthy controls performed the grip force task equally well without being fatigued. In patients, task-related activity in lobule VI of right motor cerebellum changed in proportion with individual FSMC_MOTOR scores. In right dorsal premotor cortex, linear increases in activity across consecutive task blocks scaled with individual FSMC_MOTOR scores in healthy controls, but not in patients. In premotor and dorsomedial prefrontal areas, patients were impaired at upscaling task-related activity the more they were affected by motor fatigue. The results support the notion that increased sensorimotor processing in the cerebellum contributes to the experience of motor fatigue and fatigability in multiple sclerosis. Additionally, downscaling of motivational input or sensorimotor processing in prefrontal and premotor areas may constitute an additional pathophysiological factor.